The present invention relates to superconductor devices, and, in particular, to a superconducting switch.
It is known that, in order to cause a superconducting material to shift from the superconducting state to the normal-conducting state, either all or part of the circuit must be subjected to a magnetic field or to a temperature rise, the value which exceeds that of a given field or of a critical temperature. The material thus loses its superconducting properties and reverts to the normal state in which it has electrical resistance. Similarly, by restoring the conditions of field and temperature to their initial state, the material returns to its zero resistance state the same manner as a conventional arrangement which makes use of a mechanical switch or the like.
One type of superconducting switch is called a cryotron which comprises a gate-conductor film on the order of 0.3-1.0 micron thickness of soft superconductive material which is crossed by narrow control-conductor film also on the order of 0.3-1.0 micron thickness insulated therefrom and preferably formed of hard superconductive material. Both the gate-conductor and the control-conductor are thus normally in the superconducting state. If sufficient current is caused to flow through the control-conductor, the resulting magnetic field causes the gate-conductor to become resistive in the region of the crossover. See U.S. Pat. Nos. 3,383,758 and 3,706,064 which are incorporated by reference.
Other types of superconductor switches use an interface region between two superconducting regions. The interfacial region may be formed in a variety of geometries including a superconductor, insulator barrier, superconductor (SIS); superconductor, normal metal, superconductor (SNS), point contact and bridge type structures. The interfacial region in each of the above cases is a weak-link region interconnecting the superconductive regions, the weak-link is the thin insulator in the SIS structure, the thin normal metal in the SNS structure, the region of contact in the point contact structure and the region of minimum cross-sectional area in the bridge structure.
When the current through the interface exceeds a first critical current, I.sub.c, the voltage across the interface increases to some finite value. This voltage does not return to zero until a switchback current is reached.
The switching in the above devices is magnetically controlled.